What is it?

Rez is a unique synthesizer program for the Nintendo Gameboy. It crudely simulates a resonant filter in a way inspired by the resonance algorithm used by the Casio CZ series phase distortion synthesis. Whether I’ve come close to this type of synthesis, I leave to the users of the program to decide. It can both produce sounds meant to emulate this effect, and sounds more reminiscent of a hard sync oscillator. It also produces a graphical pattern on the Gameboy screen.

During the development of this program, I’ve encountered a number of subtle issues with the DMG hardware, which you can either see as bugs or charming features of the hardware being (ab)used.

What should you run it on?

Rez is intended to be used on real hardware, in particular on a DMG, the original “brick” variety of Gameboy. If you wish to use an emulator, BGB and Gambatte are good choices.

Honorary mentions go out to no$gmb, TGB Dual and smygb02 for sounding glitchy in ways that may be interesting, even though they sound nothing like intended.

How does it work?

In this version, the controls are simple. Up and down control the “resonant frequency”. Left and right control the “fundamental frequency”. Currently, the synth is not tuned to any scale, so you need to manually tune it if you wish to use it with other instruments.

The values of these parameters are shown on the screen: The four hex digit value is the resonant frequency and the two hex digit number is the fundamental frequency.

A and B toggles between different waveforms which gives the resonance a different character, from relatively smooth to harsh to a hard synced sawtooth oscillator.

On the far right (press A you can’t get any further) there’s a clean sawtooth waveform. This waveform is unaffected by the resonant frequency setting and may be useful for tuning the fundamental frequency to another instrument.

There’s a bug in the DMG hardware which sometimes causes the waveform stored in the channel 3 wave RAM to be corrupted. You can press start to enable a workaround for this issue, at the expense of a slightly different timbre. You may also choose to leave this off which randomly and radically changes the waveform.

Pressing select shows the current contents of the wave RAM. This is a debug feature that I used to debug the wave RAM bug. It may be of interest if you’re curious.

All buttons can be used simultaneously.
TIP: Find a “sweet spot” resonance and fundamental setting and alternate between holding left+up and right+down. This increases one setting and decreases the other. This can give some nice effects.

Future versions

I have plans for more features for Rez, including among other things better ways of controlling the parameters. I don’t want to promise too much yet, but MIDI input support (using Arduinoboy or Nanoloop MIDI-USB) may be plausible. But I felt that I wanted to get a version of this out the door to avoid tweaking the program indefinitely and never releasing it.